1. Field of the Invention
This invention relates generally to the field of corrugated materials, and more particularly concerns the field of corrugated materials suitable for packaging applications.
2. Description of the Prior Art
Corrugated packaging materials are well known. One common corrugated material is known as "single faced corrugated board". Single faced corrugated fiber board is made by gluing a flat sheet of liner board to a sheet of corrugating material, known as a medium, which has been passed through a "single facer" and formed into a series of arches, or flutes. Although it is resistive to compressive forces exerted longitudinally of the flutes and to forces which would bow the flutes, single faced corrugated board may be flexed in two directions without structural damage, and may be rolled into cylindrical rolls, wherein the flutes run parallel to the longitudinal axis of the cylinder, with either the facing or the corrugating medium on the outside of the roll. Generally, single faced corrugated board is rolled with the corrugating medium to the inside. Single faced corrugated board is typically used as a packaging and cushioning material in which products may be wrapped.
A second common corrugated material is known as "double faced corrugated board". Double faced corrugated fiber board is made by gluing one flat sheet of liner board to each side of the corrugated medium. The fluted construction gives strength and rigidity to the fiber board and serves as a cushion for anything which comes in contact with it. More than 90% of all corrugated boxes are manufactured from double faced corrugated board. It is also used in the form of liners, pads, shelves, and partitions for the inner packing of glassware and other fragile articles which require protection, as well as a multitude of other applications.
Double faced corrugated board is substantially rigid in all directions, and may not be rolled without "breaking" one or both faces. Breaking occurs when the board from which one of the faces is constructed permanently buckles, or creases, between the spans of the flutes in the corrugated medium. Once a face has been broken, the double faced corrugated board loses its planar rigidity.
Since double faced corrugated board may not be rolled for storage and shipping without destroying its structural properties, it must be shipped in flat sheets, which are more difficult to handle than rolls.
Single faced corrugated and double faced corrugated board are generally constructed of fiber board. The facings and the corrugated mediums are glued together with a starch base or comparable glue. Occasionally, fiber board is coated or impregnated with wax or plastic to create a waterproof board. More recently, single faced and double faced corrugated board have been constructed from plastic and appropriate adhesives. Such a board is the "TRU-COR".TM. plastic corrugated board produced by the Menasha Corporation. Another recent development is a fluted, double faced sheet that is extruded from a thermoplastic, which resembles double faced corrugated fiber board. An example of this product is "PRIME COR-X".RTM. sheet, produced by the Primex Corporation of Oakland, N.J. These materials have properties similar to corrugated fiber boards, in that single faced corrugated plastic board is rollable, and has good cushioning properties, and double faced corrugated plastic board, or double face extruded plastic board is substantially rigid in all directions, and is not rollable without "breaking" one or both faces of the board.